In the micro-electro-mechanic systems, the preparation of deep grooves or deep cavities in the semiconductor material, such as a silicon dice, is very important. The applications of such deep groove and cavity structure include forming a micro fluid channel in the micro structure of silicon dice. In the preparation of grooves or cavities which are as deep as tens of micrometers, the planarization of the grooves or cavities is always a great task. Difficulties are noted especially when the micro fluid channels are as deep as about 30 .mu.m.
In the conventional art, there are four major approaches in the planarization of the deep groove or deep cavity structures. They are:
1. Dual photoresist and two-step etching technology. In this approach, a first photoresist layer is filled within the shallow trench formed on the dice and then a second layer of photoresist is applied on the surface of the dice for the whole area. After a two-step etching process, a planarization structure may be formed on the dice. (See U.S. Pat. No. 5,516,625, "Fill and etch back process using dual photoresist sacrificial layer and two-step etching process for planarizing oxide-filled shallow trench structure.") PA1 2. Spin-on glass (SOG) planarization: In this approach, a layer of SOG is applied on an assembly of multilevel die and the assembly is etched such that the etching rate of the SOG layer is the same as that of the dielectric layer under the SOG layer. As a result, a planar surface may be formed on the rugged surface of the die. A second dielectric layer is then deposited and the planarization is achieved. (See U.S. Pat. No. 4,676,867, "Planarization process for double metal MOS using spin-on glass as a sacrificial layer") PA1 3. Silicon fusion-bonding technology: In this approach, the planarization structure of deep grooves may be obtained by using silicon fusion bonding technology. (See K. Petersen et al., "Silicon fusion bonding for pressure sensors", Tech. Dig. IEEE Solids-State Sensors Workshop, SC, pp. 144-147, 1988.) PA1 4. Sacrificial wafer bonding technology: In this approach, the planarization structure of deep grooves or cavities can be formed using sacrificial wafer bonding technology. (See V. L. Spiering et al., "Sacrificial wafer bonding for planarization after very deep etching", J. Microelectromechanical Systems, 4, pp. 151-157, 1995.)
Among the above-mentioned approaches, the first two may not be applied in the planarization of grooves or cavities as deep as tens of micrometers. Although the latter two approaches may be applied to deep groove structures, they inherent some disadvantages. As describe above, in the latter approaches, grooves or cavities are formed on the silicon substrate first and a planarization layer is bonded onto the substrate. During the bonding of the planarization layer, the environment shall be strictly clean. In addition to this, both approaches are very sensitive to the surface treatment processing conditions of the die. As a result, complicated preparation processes and high preparation cost are inevitable.
It is thus a need in the industry to provide a novel planarization technology to be applicable to deep groove or deep cavity structures formed in semiconductor substrates.
It is also a need to have a simplified planarization technology for deep groove or deep cavity structures for semiconductors.